1. Field of the Invention
This invention relates to an efficient method for producing, transporting, offloading, pressurizing, storing and distributing to a marketplace a natural gas which is produced from a subterranean formation remotely located relative to the marketplace utilizing a subterranean formation capable of storing natural gas.
2. Brief Description of the Prior Art
Because of its clean burning qualities and convenience, natural gas has been widely used in recent years both for industrial use and for home heating. Many sources of natural gas are located in remote areas, which are not conveniently available to any commercial markets for the natural gas. When pipelines are unavailable for the transportation of the natural gas to a commercial market, the produced natural gas is often processed into liquefied natural gas (LNG) for transport to market. One of the distinguishing features of a LNG plant is the large capital investment required for the plant.
A further large investment is required at the destination for the LNG for cryogenic storage tanks near the marketplace to store the LNG until it is marketed. Such cryogenic facilities are relatively expensive and require re-gasification of the LNG for distribution via a pipeline system or the like to the ultimate consumers.
Where pipelines have been available to deliver natural gas to a marketplace, the demand for natural gas has fluctuated widely between low demand periods and peak demand periods. In such instances, natural gas has, in some instances, been stored in subterranean formations or cavities. The natural gas is delivered as a gas to the subterranean storage and subsequently retrieved from the subterranean storage for delivery to a pipeline or other system to distribute it to the ultimate consumers. These systems require that natural gas be available as a gas from pipelines for storage in the subterranean storage areas.
Natural gas is typically available at pressures from about 250 psig (pounds per square inch gauge) to about 10,000 psig at temperatures from 80 to about 350.degree. F. from many subterranean gas-bearing formations. This gas is readily processed by well-known technology into liquefied natural gas. Various refrigeration cycles have been used to liquefy natural gas with the three most common being the cascade cycle which uses multiple single component refrigerants and heat exchangers arranged progressively to reduce the temperature of the gas to liquefaction temperature, the expander cycle which expands gas from a high pressure to a low pressure with a corresponding reduction in temperature, and multi-component refrigeration cycles which use a multi-component refrigerant and specially designed heat exchangers to liquefy the natural gas. Combinations of these processes have also been used. LNG is typically transported by sea in cryogenic tanker ships.
As noted previously, both of these methods entail certain disadvantages, i.e. the transportation of natural gas by pipeline is limited by the availability of the pipeline system; therefore, the storage of natural gas in gaseous form in subterranean formations, cavities or surface storage facilities is limited to those areas in which greater quantities of natural gas can be delivered, then can be used during low demand periods. Similarly, the use of liquefied natural gas, which is liquefied at or near the marketplace, is also limited to those areas where an excessive amount of natural gas can be delivered during at least a portion of the year. As indicated previously, this practice also requires the construction and use of cryogenic tanks, which are relatively expensive.
The use of liquefied natural gas which has been liquefied at a production site at a remote location also requires the use of cryogenic storage space and re-gasification equipment at or near the marketplace so that the LNG can be stored until it is desired to re-gasify the LNG and use it.
As noted above, various systems for producing liquefied natural gas from natural gas are well known. Some such systems are shown, for instance, in U.S. Pat. No. 4,033,735, issued Jul. 5, 1977 to Leonard K. Swenson, and U.S. Pat. No. 5,657,643, issued Aug. 19, 1997 to Brian C. Price, and U.S. Pat. No. 3,855,810, issued Dec. 24, 1974 to Simon et al.
Re-gasification systems for re-gasifying liquefied natural gas are also known. These systems can vary widely but include systems such as open rack vaporizers which are typically used with seawater as a heat exchange medium, shell and tube vaporizers which use either seawater, glycol-freshwater mixtures, or propane and an intermediate as the heat exchange medium. Submerged combustion vaporizers, steam-heated vaporizers and ambient air heated vaporizers are other means for re-gasifying liquefied natural gas. A wide variety of vaporizers can be used so long as they are effective to re-gasify the LNG by heat exchange with some suitable heat exchange medium.
Accordingly, in view of the expense of delivering the natural gas to consumers by either of the foregoing methods, continued efforts have been directed to the development of more efficient methods for delivering natural gas from a remote production site to a marketplace more efficiently.